It is known that membranes for pressure accumulators should exhibit both flexibility and imperviousness properties so as to allow a good transmission of pressures between both compartments containing the liquid and the gas, respectively.
There has already been proposed resilient membranes made from different materials and in this respect reference should be had for instance to the French patent application publication No. 2,443,622 and to the French patent No. 1,494,473.
However, the known membranes manufactured for instance from a thermoplastic material of the polyurethane kind exhibit an imperviousness to gases which is imperfect, which results after some years of use on a vehicle in a drop of the gas pressure prevailing inside of the sphere fitted with the membrane or diaphragm, so that the sphere has to be replaced to preserve the desired characteristic features.
On the other hand are known materials having a satisfactory imperviousness to gases such as nitrogen but the membrane flexibility then becomes unsatisfactory.